In a model driven architecture (MDA) platform independent models (PIMs) are transformed into platform specific models (PSMs). In a typical scenario, the PIM expresses high-level requirements, while a PSM expresses their implementation over specific technologies, and resources. Initial applications of the MDA architecture have focused on patterns and transformations that work on computer program source code. For example, a model of a Java class may be transformed by applying the singleton pattern to generate a static instance, and a static method for creating and retrieving it. Similarly, an XML declaration of object type can be transformed into a Java RMI-based distributed object implementation deployed on WebSphere hosted on an AIX server. Existing tools, such as IBM Rational Software Architect (RSA), and Microsoft Visual Studio require that users first select the pattern or transformation to apply, and then bind its parameters. In the singleton example, an RSA user must first drag and drop the “Singleton” pattern from a pattern explorer tree to the model diagram and then drag and drop the class onto the pattern node.
MDA is increasingly being applied to new domains that go beyond source code transformations. For example, model transformations have been used to design the deployment of composite applications. A Logical Application Structure PIM is transformed using fine-grained “best-practice” transformations into a datacenter Deployment Topology PSM. Applying MDA approach in such as a domain is significantly more complicated for the following reasons:                Transformations may take several parameters, typically, a set of model elements.        Per-conditions for the execution of a transformation may exist. For example, a precondition may state that an input pair of model objects is connected via a link in the current model instance.        A sequence of model transformations may need to be applied on a PIM instance model in order to obtain a PSM for it.        There may be many PSM instances that can be reached from a given PIM instance by applying (different) sequences of transformations.        PSM instances that are reachable from a PIM in this way may vary in their quality, relative to some objective function.        Some model transformation sequences may lead to a model that is not yet a PSM but that cannot be further modified by applying transformations from a given set.        
The approach of applying model transformations to map a PIM to a PSM guarantees correctness by design. However, selecting the best transformation to apply in a given state is a challenging task. While the selection of transformation to apply may depend on domain knowledge and domain preferences, the user can benefit from guidance and help in identifying the best transformation choice at a given model state. In particular, the user may want to filter the set of transformations according to multiple criteria such as: (1) what transformations are valid at a given state (2) what transformations take as an input model objects from a particular subset (3) what transformations affect model objects in a particular subset.